Combination wrenches are used to tighten or loosen fasteners. The industry standard for this type of tool is a single handle with a box-end shape on one end of the handle and an open-end shape on the opposite side of the handle. The original box-end shape was a solid unit with no moving parts. Such a design required the operator to lift, rotate and reset the wrench for each stroke of the tool. This is a time consuming process and the solid unit was replaced with a ratchet gear system that utilizes a driving gear with a spring loaded pawl. The pawl enables the operator to apply toque in one direction and to slip in the opposite direction. The reciprocal motion of the handle allows the wrench to maintain continuous contact with the fastener during the tightening or loosening process. The ability to maintain constant contact with the fastener is a major advantage over a traditional wrench because labor is significantly reduced.
The ratchet mechanism has drawbacks including friction between the pawl and the driving gear. Both have a set of teeth which engage and lock during the torque stroke. Additionally, the pawl teeth rub against the driving gear during the slip or back throw process. Such rubbing action creates friction and deteriorates the efficiency of the wrench. Over time the teeth can wear down and will require replacement. In addition, ratcheting mechanisms are indexed and require a large back throw between handle swings, which creates a problem with there is insufficient room for the handle to operate.